


The Lake's Secret

by Kou_91



Category: Natsume Yuujinchou | Natsume's Book of Friends
Genre: Alternate Universe - Fantasy, Body Worship, M/M, Voyeurism, aged-up natsume, matoba gets some tail, mermaid natsume, self indulgent OOC healthy(?) relationship AU matonatsu, unnecessarily gratuitous description of a mermaid's body, youkai natsume
Language: English
Status: Completed
Published: 2018-06-04
Updated: 2018-06-04
Packaged: 2019-05-18 00:40:45
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,418
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14842289
Author URL: https://archiveofourown.org/users/Kou_91/pseuds/Kou_91
Summary: Every morning before dawn, Matoba visits the beautiful koi ayakashi who lives in the lake near his clan’s hunting grounds. The ayakashi, Natsume, begrudgingly allows the visits, but only because the exorcist always brings gifts of Natsume’s favorite flower, which grows too far inland for him to reach himself from the water…(WARNING: Includes image of sensually-posed mermaid!Natsume, so watch your screen if you're trying to discreetly read spicy fics in public.)





	The Lake's Secret

**Author's Note:**

  * For [Yumemikki](https://archiveofourown.org/users/Yumemikki/gifts).



> Many months ago I got Mikki as my giftee in a Secret Santa gift exchange with friends. He requested Mermaid!Natsume MatoNatsu, and last week I FINALLY drew him the fan art below as his gift.
> 
> But as I was drawing it, this story appeared in my mind, and I decided to write it as an extra gift to apologize for making him wait so long! X'3
> 
> Mikki, I hope you like it as much as you liked the drawing! And other readers, I hope you enjoy it, too!

\----------

Crouching low within the tall grass near the water’s edge, Matoba is careful to remain concealed by the overgrown plants and the darkness of the early morning hours as he waits staring at the lake ahead. The water is still save for the glistening of the moon’s reflection on its surface, but during this threshold between night and day, when most of the surrounding forest’s creatures have yet to wake, such silence is to be expected.

But he knows he won’t be alone much longer.

Deciding it’s safe to look away for now, he glances down at the bundle of purple star-shaped flowers clutched in his hand. Even when illuminated only by the pale moon, their color is rich and vibrant. And their petals, always five each, are flared and lovely and perfectly spread apart as if inviting an embrace. With such an endearing and delicate appearance, Matoba understands why the one he brought them for adores them so much. Hopefully he brought enough today.

The exorcist’s ears perk when he hears the sound of something (or rather, someone) surfacing from the water. He crouches deeper into his hiding place, careful not to disturb the surrounding plants and stones lest he risk discovery. Keeping motionless save for his trembling breath, he gazes ahead in anticipation. He knows from experience to train his eyes on the gnarled tree that has grown from the center of the lake… because that is where he always appears.

Matoba’s breath catches as dainty pale fingers extend from the water’s surface. Followed by a slender wrist, the fingers gently curl around a vine hanging from a low tree branch. The vine pulls taut, and the exorcist watches as two bone-white horns pierce through the lake. The hand pulls tighter on the vine, and all at once, he emerges. The object of Matoba’s unrequited affection.

A beautiful koi youkai with cascading waves of golden hair, skin fairer than the strands of freshwater pearls adorning his neck, amber eyes as cold as they are firey, and the most conspicuous feature of all: a shimmering tricolored tail framed with layers of translucent fins that flare off his hips like the train of a skirt framing his tail’s sleek silhouette. The ayakashi perches on a low branch of the warped tree, the end of his tail still dipped underneath the lake’s surface. With calico patches of white, orange, and black, it sways to and fro as it rhythmically swirls the water below.

Matoba smiles to himself as the youkai’s waking ritual begins. The koi sweetly brushes the sleep from his eyes as he shakes his head from side to side, water droplets scattering from his hair, sparkling like crystals dropping into the lake below. Knowing what comes next, Matoba peels back the paper seal over his right eye so he can see with both as the youkai extends his arms, arching his back in a luxurious stretch. Matoba reminds himself to breathe as he watches the wet droplets on the ayakashi’s skin glisten in the moonlight as they drip down to trace each graceful curve of his lithe body. He yawns, forgetting to cover his mouth at first (as he always does), before quickly clapping his hand over it, eyes darting from side to side before he sighs in relief that he wasn’t seen. Or so he thinks. 

But the exorcist’s favorite part has only just begun. The youkai reaches behind to gather the silken waves of his hair over his shoulder, pulling it to the front for its daily grooming. After he wrings out the excess water, he checks the strands of pearls threaded throughout, adjusting any that became loose as he slumbered. After combing out the length with his fingers, he produces a small woven basket he had nestled in one of the grooves of his tree. He takes out one of his beloved purple Chinese bellflowers, and uses its stem to deftly twist it into a lock of his hair. 

Looking back into the basket, the youkai frowns and the exorcist grins. It’s empty. Just as Matoba suspected it would be by today.

Careful not to miss his cue, Matoba swiftly retrieves a paper butterfly from his sleeve. He hastily fastens one of the flowers he brought to the small shiki, sending it off with a harshly whispered command.

“Go… quick!”

The paper insect flutters past the koi as it gently drops the flower into the basket, eliciting a small, surprised gasp from the ayakashi. Without looking up, the blond glares at the flower as he takes it in his hand, fastening it to his hair with an exasperated groan.

“Show yourself, exorcist…”

“Too obvious?” Matoba calls out with a sheepish laugh.

“Always…” The koi sighs with a shake of his head.

Rising from his hiding place, Matoba carefully navigates the loose stones at the water’s edge as he approaches the lake. Kicking his wooden sandals off in haste, he keeps his bouquet of flowers safely pressed to his chest as he slips into the (colder than expected) water. His robes billow around him as he wades towards the tree, thankful to the gods that the thing grew in the shallow end. The youkai watches with his chin rested in one hand, the other hand open and reaching towards the exorcist, expectantly waiting.

Finally arriving at the youkai’s side, Matoba grins as he holds a flower up in offering. The bloom is accepted, but his smile is not returned (it usually isn’t). He watches in adoration as his gift is added to the ornaments in his darling’s hair, and he holds up another flower only for it to be snatched away without a word of gratitude. The beauty’s especially callous manner towards him this morning stings, but Matoba is quickly consoled when he realizes his hands are now free for other things. 

Eyeing the koi’s elegant tail, he subtly moves closer. Positioning his hand on what would be the back of the blond’s thigh if he had legs, Matoba takes a lustful stroke down the tail’s length. 

“Don’t touch.”

Matoba grunts as a fin he had just been lovingly tending to swats him back. Those things are stronger than they look.

“I see you’re especially cold this morning...”

“No I’m not. Do you have any more?”

Matoba dutifully reaches into the sleeve of his robes, producing more flowers. After accepting the offering, the youkai uses his tail to push the exorcist back even further, having taken what he needs from him.

As the koi continues twisting the bellflowers into his locks, he murmurs absentmindedly, more to himself than the exorcist. “You brought so many… I suppose you’re not entirely useless. They grow too far inland for me to get them myself...” His focused expression changes to a flustered gape when he feels another grope on his fin, this time from underneath the water’s surface. The exorcist is clever today. Protectively drawing his tail back towards himself, the youkai hisses.

“Why are you so interested in my tail right now?”

“I’m interested in all of you, but you’re sitting too high for me to reach anything else... Please come down.” 

“I don’t feel like it.”

Sighing in disappointment, the exorcist pouts. “You really don’t think you’re harsher towards me than usual today? Because I do…” Moving forward to close the distance between them, he cautiously wraps both arms around the koi’s tail, resting his cheek against its side. Although he knows it’s risky, his allows his voice to take a teasing tone as he purrs: “Perhaps you’re just angry I didn’t visit yesterday?”

The youkai’s body tenses.

“Well…” The blond shakes his head as if to test whether the flowers are secure in his hair. He peers down into the water, pretending to be too busy checking his own reflection to look at the exorcist. “Why didn’t you come yesterday?”

“I had to work...” Matoba responds, gingerly stroking the koi’s tail as if to soothe him. He’s careful not to go against the grain of the scales. He learned the hard way that the youkai doesn’t like that. And that he himself doesn’t like taking a fin directly to the face.

“Please come down… I can’t stay long this morning.”

Matoba’s heart jumps in his chest as he feels the youkai’s slick body begin to slide down his cheek, his breath catching as the surface transitions from scales to skin. When their chests align, the youkai wraps his arms around Matoba’s neck, and the exorcist accepts the invitation to hold him like a bride, his iridescent fins floating to the water’s surface and giving the appearance of a glowing wedding veil.

Having gone slightly weak in the knees, Matoba leans against the tree behind him as he looks down to take in the view of the lovely ayakashi up close. His beauty is always breathtaking, but today he’s especially so, having decorated his body and long golden hair with braids of pearls and flowers in all the right places. 

“To think you’ll let me hold you like this but you won’t tell me your name…”

Reaching back to brush a lock of hair away from his face, the koi sighs. “No ayakashi is foolish enough to give their name to an exorcist regardless of the nature of their relationship, Matoba-san.”

The exorcist smirks. “Oh? Well, what if I already knew it? Perhaps I did come here yesterday and the reason I didn’t show myself is because I had the misfortune to arrive at the same time as your frighteningly large white wolf friend again. And perhaps this time I overheard him call you ‘Natsume’…?”

Natsume’s brows furrow in irritation. This exorcist really is annoying.

“Then I suppose you might as well call me “Natsume,” then. You’re wiser than I thought, you know. You made the right choice to stay hidden when Madara-sama was here. I’ve made him aware of our arrangement, but he would have eaten you alive had he seen you.”

“So you forgive me for yesterday?” Matoba smiles triumphantly as he nuzzles one of Natsume’s horns. The koi growls as he covers them protectively with one hand and pushes the exorcist’s face away with the other. Matoba should know better than to touch them like that. Natsume has told him they’re sensitive. But he can’t resist the way Natsume’s cheeks flush when he does.

“I do not. And speaking of our arrangement, look at the state of these seals! Half of them have fallen from the trees and are littering my lake. I can sense exorcist activity drawing nearer every day. I only tolerate your presence because you promised to protect me and the neighboring youkai from other exorcists, but you can’t do that with broken seals, can you?”

Reluctantly looking away from Natsume to assess the state of the spells and traps he had set up around the lake, Matoba laughs nervously. They really are a mess.

“I promised to protect you and I will. I’ll repair them as soon as possible.”

“Good. And when you do, make sure to leave one of those letters so I know it was you.”

Matoba looks down at the tree behind them, frowning as his eye locates a collection of letters gathered in a pile in the same groove low in the tree trunk where Natsume keeps his basket. Matoba sends these letters from the shore using butterfly shiki from time to time for various reasons… Sometimes to let Natsume know when dangerous exorcists are nearby, and sometimes just to let him know he misses him on days Natsume refuses to come to the water’s surface. Of course, each one remains sealed and unread.

“You won’t read it even if I leave one… You never do.”

“They’re too long.”

Matoba laughs as he steps back, finding a branch of the gnarled tree located low enough for him to sit on. “For such an ancient youkai, you make excuses like a human child…” Pulling Natsume into his lap, he leans over the blond, cupping water in his hand to trickle over the youkai’s tail to keep him comfortable. Patting the scales to ensure each is sufficiently damp, he repeats the loving gesture at a leisurely pace. Sighing in pleasure at the gentle touch, Natsume clutches the collar of Matoba’s robes, small hands squeezing at the fabric.

“Natsume-kun… You know if you read them, they might keep you company on the days I can’t visit. Isn’t that preferable to waiting around for me all day, seething in anger as you wonder where I am, and then wasting part of our precious time together treating me so meanly once we’re finally reunited?”

Natsume’s silence prompts Matoba to peek at the koi through the corner of his eye to check whether his teasing has gone too far yet. Natsume’s own eyes are downcast, shielded by his blond lashes to avoid the exorcist’s gaze. He’s worrying his bottom lip, and with the way his cheeks are tinted red, Matoba can tell he’s close to his limit. But a bit more shouldn’t hurt.

Under the pretense of continuing to keep Natsume’s scales wet, Matoba lets his hand slowly slide down to the backside of Natsume’s tail. Rubbing his hand in a circular motion, he smirks to himself as he observes that the shape of the youkai’s rear is more like a human’s than expected. He politely pretends not to hear Natsume’s quiet moans against his neck as he dares to move his hand more towards the center, his eyebrow twitching in intrigue upon the realization that there is a cleft down the middle.

When a squeeze of his hand elicits an enticing whimper from Natsume, he can’t control himself any longer. Pressing his lips to the shell of Natsume’s ear, he whispers. “Some of those letters’ contents are quite thrilling, you know… you might find yourself falling even more deeply in love with me if you knew what they said about the kind of things I’d like to do to you… But be careful, you’ll break my heart if you stay up all night reading them and you end up sleeping so late you miss our morning visit.”

Ah, he crossed a line. Natsume gasps and pushes free from Matoba’s hold, submerging himself back into the lake. The exorcist looks down, scanning the water waiting for him to resurface. Finally, he sighs in disappointment when he hears Natsume rise behind him on the opposite side of the tree where the water’s deep end begins.

“Now that I know those letters say that kind of thing, I’ll never read them for sure! And just so you know, I don’t sit around all day waiting for you on the mornings you don’t show up. And most of all, I’m certainly not in love with you!”

With that, Natsume turns to swim slightly further into the deep end, his tail splashing water into Matoba’s hair.

“Of course. Pardon my misunderstanding…” Matoba winces when the morning sun shines into his eye, alerting him it’s time to leave for work. He pouts at the unfortunate timing as he slips back into the shallow end of the lake. Before he can begin wading back towards the shore, the sound of a small voice prompts him to turn around.

“The sun is up already?”

Peeking out from his hiding place behind a stone, the youkai gazes wide-eyed at the sunrise. With the way his lower lip is pushed out in a pout, Matoba can tell he’s disappointed, too. But he knows better than to mention it now, Natsume has had more than enough teasing this morning.

“You know if you’d come live in my pond like I keep asking, I wouldn’t have to leave so soon… and I’d never miss another visit.”

“Why would I go live in your pond when I can live in my lake?” The koi retorts.

“I suppose I can’t argue with that.” Matoba laughs as he turns back around to leave. But he only makes it halfway to the shore when Natsume suddenly emerges from the water in front of him to block his path.

“These purple flowers,” he says, gesturing to one tucked behind his ear. “...do they grow near your pond?”

Matoba nods eagerly, his grin wide with hope. “They do. And some of them grow so close to the water’s edge you could pick them yourself.”

“In that case, I never want to live in your pond, then. You do such a good job of picking the flowers without damaging the stems, I prefer for you to do it. But you might not pick them for me if you think I can get them on my own.” 

Defeated by the ayakashi’s trick, Matoba buries his face into the crook of Natsume’s neck, wrapping his arms tight around his waist. “You really are too cruel today…”

The youkai grunts in irritation when the exorcist allows his body to go limp in Natsume’s arms, relying on him to do all the work as he sways his tail to slowly propel them to shore. The exorcist is always so dramatic when it’s time to leave. As Matoba climbs onto the land, his soaking wet robes cling to his body as he turns on his knees to offer one final proposal to his would-be lover in the water below.

“What if I just brought you to my pond for a visit? You might like it. And if you do, then it will be your pond. But if you don’t, I promise I’ll bring you back here if it isn’t to your taste.”

Natsume appears to consider the question for a moment, but Matoba huffs in disappointment as the koi sinks back into the water without a response.

But before Matoba can rise to his feet, Natsume suddenly emerges back through the water with a splash, clutching the collar of the exorcist’s kimono with one hand, and wrapping the other arm around his neck to pull him down. As their faces draw suddenly nearer, Matoba closes his eyes in anticipation of a kiss, but Natsume’s lips brush by his cheek to rest at his ear instead.

“The flowers you brought should last me a few days. So bring me something else from your pond tomorrow, alright? Something that might change my mind.”

With that, Natsume releases Matoba, sinking back into the water without a sound.

\----------

The next morning before sunrise, Matoba is back at his hiding spot by the lake’s edge. Deciding there’s no need to conceal himself when he’s received an invitation for once, he sits on a large stone while he waits for Natsume to rise from his slumber. Matoba himself is already exhausted, having arrived an hour earlier to repair the seals for Natsume as he promised. But his fatigue doesn’t dampen his spirits.

Instead, he smiles in anticipation as he looks down at the gift he brought for Natsume today. A small sprig of freshly-bloomed sakura flowers. Natsume has certainly never seen these before since there are no sakura trees around his lake. Natsume loves flowers so much that when Matoba tells him his pond fills with these pink petals for two weeks every year, surely he will agree to stay in Matoba’s pond at least during the spring?

Matoba sighs to himself as he imagines what it would be like to be able to see Natsume from his own tea room every morning. Combing his golden hair, gathering flowers along the edge of the water, swimming in circles, playing games with the fish in the water...

The exorcist’s heart is bursting with anticipation. He can’t wait another moment to see Natsume today. He kicks off his sandals and stands at the edge of the water, waiting for any sign that Natsume may be awake. The sky is turning light, their visit is already getting cut short today. Why won’t he come out?

The answer becomes clear when the sunrise illuminates Natsume’s tree.

A certain pile of letters appear to be missing. Someone must have retrieved them. And that someone probably stayed up all night reading them. Matoba shakes his head with a chuckle as he turns to leave for work, but he pauses when he spots something from the corner of his eye. Natsume’s grass-woven basket is sitting on the shore at his feet.

Matoba gently places the twig of sakura flowers inside before he walks away, smiling to himself as he plans how best to tease Natsume for this tomorrow.


End file.
